The Census2011Geog project

Background

The geographical areas which were used to publish aggregate data from the 2001 Census in England and Wales were designed to be optimal for the spatial distribution and socio-economic characteristics of the population at that time. In a minority of areas, these distributions and characteristics had changed significantly by the time of the 2011 Census, making the existing geographies unfit for the release of 2011 data.

Aims

The Census2011Geog project was funded by the Economic and Social Research Council (ESRC) as part of the ESRC Census Development Programme and ran from 1 June 2008 to 31 January 2010. It aims were:

(1) To develop automated procedures for maintaining (splitting, merging, re-designing) the 2001 Census output geographies in order to create 2011 output geographies for England and Wales

(2) To assess the implications (in terms of achievement of optimal solutions, statistical characteristics of resultant zones, and effects on data linkage) of using different building blocks (such as postcodes and street blocks) for these maintenance procedures.

Key findings

The Census2011Geog project conceptualised the problem and carried out detailed investigations of confidential 2001 and contemporary population data in order to ascertain the number and types of areas likely to be unfit for purpose in 2011. It further developed existing software to create a tool (AZTool) which automatically splits, merges or redesigns areas which are found to be over- or under-threshold (i.e. containing too many or too few people and/or households) at the time of the 2011 census. The project proposed an iterative process of maintenance, starting with output areas and then moving on to the higher levels of output geography, sequentially relaxing specified design criteria as required. It recommended the use of postcodes as the building blocks for the maintenance process.

Implementation

The evidence base provided by the project informed policy decisions taken by the Office for National Statistics (ONS) for the 2011 Census, and its software and methods were subsequently implemented by ONS to create the 2011 output areas for England and Wales, which were released in October 2012.